The invention relates in general terms to an apparatus for cooling hot material which is, for example, discharged from a kiln.
A cooling apparatus of the general class to which the invention relates is used to cool particulate material (e.g., cement clinker or other mineral materials), which has been burnt in a kiln. Such apparatus can comprise traveling grate coolers, thrust grate coolers, and the like. The hot particulate material discharged from the kiln outlet typically undergoes quenching in the material inlet part of the cooling apparatus and is then moved, distributed as well as possible, to consecutive rows of grates on which additional cooling is then carried out while the material to be cooled is transported along a path extending from the material inlet to the material outlet of the cooler on said grates. Typically, the cooling air which is blown through the hot material in the recuperation zone of the cooling apparatus is then reused or recycled further generally as air for combustion in the preceding kiln.
Grates for cooling or combustion are generally equipped with overlapping rows of grate plates, of which some are mounted in a fixed position and others are reciprocating, which generally means that they oscillate in a longitudinal direction, with the forward stroke of the oscillation being the direction in which the particulate material to be cooled travels through the cooler, and they thereby serve in part to facilitate the movement of the material through the cooler. The grate plates are mounted on a carrier beam which is transverse to the direction of material flow through the cooler, with adjoining grate plates abutting. The air needed for cooling or combustion is introduced from below the grate plates through port like openings to enter, penetrate and pass through the bed of material to be cooled or burned, with said material lying on top of the grate plate.
The grate plates are subject to wear through mechanical and thermal effects. In the case of cooling grates for instance, the exposed area of the grate, which lies closer to the discharge end of the cooler, is subject to considerable abrasive wear and thermal exposure, whereas the rear, unexposed, part of the grate plate is subject to less wear, and only minimal thermal exposure.
Grate plates are provided in numerous configurations. One popular configuration is the so-called flat grate plate style, which, as its name implies, employs a flat surface on which the clinker is supported as it is transported through the cooler. In this style, ports through which cooling air passes are located on the surface of the grate. Clinker will therefore rest directly on top of the ports. There will always exist the possibility that clinker will sift through the ports, clog the air passageways and at times fall on the underlying supporting structure, causing possible damage to the supporting structure and, at times, an uneven distribution of cooling air flow resulting in a grate plate system having hot areas which can exceed metal endurance limits.
Over the years, there have been notable variations in style from the so-called flat grate configuration. One such variation, for example, is the wedge grate style in which the front area, which comprises part of the exposed area of the grate, is bent or inclined upward at an angle relative to the flat, horizontal plane of the remaining area of the grate. This design provided a partially defined area, at the point of the bend, in which the clinker could rest on the surface of the grate. This design also served to slow the flow of clinker through the cooler, which ultimately was somewhat successful in retarding red river conditions within the cooler. Air typically was distributed into the clinker through openings located in the upwardly inclined area of the grate plate. This design did not contain any anti-sifting features, as smaller particles of hot clinker could enter and clog the air distribution holes or pass through the holes into the air distribution compartments below the grate. In addition, there was only a limited tendency for the clinker to remain static within this particular design of grate. This design was utilized primarily in the mid 1950's through the 1960's.
With regard to another design of grate plate, in the early 1950's the assignee of the present invention designed and sold a particular design of a grate plate popularly known as a "pan" grate plate which in essence comprised a grate plate having on its upper surface a large depression in which clinker could be retained. The primary purpose was to retain the majority of clinker material located within the depression in a basic static condition, which thereby resulted in improved grate plate life through a reduction in wear and better resistance to red river thermal shock conditions. The grate plate could be utilized in a reciprocating or a stationary mode.
In cross-section, this prior art grate plate had a pan-like configuration, resulting in its popular name, with differing degrees of depressions with the deepest depression located in the rear of the grate plate in the unexposed area of the grate plate. The term "unexposed area", refers to that area on the upper surface of the grate plate that is, at least some of the time, covered by the overlap of a preceding grate plate. The depression was not as deep toward the front of the grate plate, that is, the portion of the grate closer to the material outlet of the cooler.
Air was distributed directly into the depression in which the clinker was held in a static condition through a plurality of air distribution holes located in the exposed, shallow portion of the grate plate. In this design, some of the clinker in the shallow area would come to rest directly on top of the air distribution holes which would potentially result in some clinker sifting into the air distribution holes, particularly during cooler fan shut down conditions.
This prior art design did not have any anti-sifting features, had high discharge velocities of air through the air distribution holes into the clinker, and, in the version sold, consisted of a single grate extending across the entire active width of the cooler which therefore necessitated replacing the entire grate in the event of excessive wear in only one area of the grate, resulting in expensive and cumbersome maintenance.